In a known hair removal system, hairs are detected by, for instance, an optical detection system. After detection of one hair, a light beam is focused on the hair so as to cut or remove it by destroying the hair root. An example of a method of cutting hair using a laser light source is known as Laser Induced Optical Breakdown (LIOB).
WO-00/62700 provides a system comprising a hair detection device and a hair removal device which is operatively coupled to the hair detection device. The hair detection device comprises an imaging device with a first image sensor. The imaging device is arranged to provide an image of a part of the skin to be treated. A control unit is arranged to discern, in the image, a hair on the skin part. The control unit is operatively coupled to the hair removal device so as to control its operation. The system includes a laser source and an adjustable beam manipulator. The image sensor comprises a CCD or a CMOS sensor.
WO-2007/013008-A1 in the name of the same applicant provides improved determination of the position and orientation of a hair and the speed at which this is done. The system is able to determine the position of a skin hair in three dimensions. A first image sensor is used to roughly determine the position and/or orientation of the hair. A second image sensor is used to more precisely determine the position and/or orientation of the hair in three dimensions. By using the sensor results of the first sensor, it is possible to limit the time required for the more precise but slower scanning operation by the second image sensor, provided the latter only needs to image a selected part of the part of the skin that is imaged by the first sensor. The selection may be carried out by the control unit which may be provided with image-processing software and/or hardware.
The first image sensor is constructed to provide a substantially two-dimensional image. Image sensors that are able to provide such information are relatively simple and operate quickly. In particular, the first image sensor comprises a 2D optical image sensor, preferably a charge-coupled device, a CMOS device or a focal plane array of photo detectors.
The light source may comprise, for instance, a LED or a laser light source. A LED is very compact and energy-efficient, and emits radiation within a relatively small wavelength band. This allows easy filtering, or any other control of radiation, where desired. Furthermore, LEDs are easily controllable and have a relatively long service life. A laser source may have a high power density and emits substantially monochromatic radiation, which is very well controllable by means of dedicated mirrors, filters, etc. Lasers are thus also suited for scan-imaging purposes. The obtainable power density is sufficiently high to cut or remove human or animal hair.
The systems described above are able to produce a light beam for removing hair. In one embodiment, the light beam may be directed at the root of the hair in order to destroy the root. The hair will subsequently drop off the skin. In this embodiment, the system includes an epilating device. In another embodiment, the light beam is directed to a target position on the visible part of the hair, i.e. the part of the hair that extends from the skin. The light beam will burn through the hair at the target position. In the latter embodiment, the system includes a shaving or cutting device.
Although the hair removal devices described above provide many advantages over the prior art, the light beam may be aimed at the same hair more than once. Aiming the light beam at the same hair is possible because the hair will remain in or on the skin after the light beam has been directed at the hair or at the hair root. The hair may then be detected twice or more times. Aiming the light beam at the same hair more than once is disadvantageous in view of an increased power consumption and possible skin damage or even injury.
A single hair may be detected, for instance, twice or more times due to the relation between the hair diameter and the resolution of the system. A hair having a diameter of, for instance, 100 μm may be detected at least four times if the system has a resolution of 20 μm. If the cutting process is induced at the center of the hair, the same hair may be detected again afterwards. For example, after cutting the hair, it is likely that the hair will not drop off, or from, the skin immediately. Subsequently, this hair may be detected and aimed at again.